Patent GB-495648-A (GB)
Title: Improvements in fluid pressure operated gear changing devices
IPC: F16H61/02
Filed: 1937-05-14
Abstract: 495,648. Variable - - speed gearing. MAYBACH-MOTORENBAU GES. May 14, 1937, No. 13716. Convention date, May 30, 1936. [Class 80 (ii)] In a suction or fluid-pressure operated gearchanging device for a vehicle change-speed gear having gear-train clutches 69, 70 and 71, 72, of the kind described in Specification 298,186, [Class 80 (ii)], for example, the gears are selected by a distributing valve 28, either manually or automatically in accordance with engine or vehicle speed by any well-known means, which supplies the pressure fluid or vacuum to power pistons 47 for actuating the gear-train clutches. The actual change, including the necessary operations of the main vehicle clutch 116, 112, is effected on release of the accelerator pedal 2. On this release of the accelerator to effect a selected change of speed, the pedal is moved by a spring 1 against a stop 7, and an arm 6, secured to the pedal, moves a sliding pin 9 to the left and by so doing closes an outlet from a chamber 16 to atmosphere and by lifting a valve 18 places this chamber in communication with a suction conduit 26 leading from the engine induction pipe 5. The vacuum from the induction pipe passes through a passage 89, chambers 87 and 83, and conduit 102 to a power cylinder 101 for operating the main vehicle clutch which is thereby disengaged. The vacuum is also passed to a selected side of the power piston 47 through the selector valve 28, the other side being opened to atmosphere, and the dog clutch member 70, 71 is thereby moved from engagement with one gear-train clutch member, for example 72, towards engagement with the other clutch member 69. Owing to the lack of synchronism, immediate engagement of this clutch pair is prevented and, with the dog clutch 70, 71 in this neutral position, the induction pipe vacuum is passed by way of an annular groove 53 in the piston-rod of piston 47 to a conduit 56 leading to a diaphragm 76 for actuating the engine throttle valve 4 momentarily to accelerate the engine, a spring connection 3 being provided between the valve 4 and pedal 2 to allow of this. This acceleration of the engine, the shaft 111 of which is shown, must be transmitted to the slower running clutch member 70, and for this purpose the main vehicle clutch 116, 112 must be re-engaged. To effect this the vacuum which passes to the conduit 56 for accelerating the engine is also passed to a chamber 80 to move a valve member 84 in chamber 83 from a seat 86 to a seat 85, the position shown on drawing. Thus the chamber 83 and the clutch operating conduit 102 is cut off from the source of vacuum and connected to a chamber 91 in which a relief valve 93 to atmosphere is situated. This valve opens to relieve the vacuum in the chamber 83, conduit 102, and iri clutch operating cylinder 101 to allow the clutch to re-engage. This re-engagement need only be light and sufficient to speed up the slow-running gear clutch 70, and a screw 94 is provided to adjust the spring-loading on valve 93 to regulate the degree of relief of the vacuum and therefore the amount of the clutch engagement. As soon as the slower running clutch member 70 attains the speed of the faster running member it is moved into engagement therewith by the vacuum still acting on the piston 47. This final movement of the piston 47 opens the conduit 56 to atmosphere through a groove 58 in the piston-rod and an aperture 60 so that the throttle 4 is returned to its closed position, and since the vacuum in conduit 56 and chamber 80 is also relieved the valve 84 is returned to its seat 86, the full vacuum thus again prevailing in chamber 83, conduit 102 and clutch cylinder 101 so that the clutch is once again fully disengaged. When the accelerator pedal is depressed to take up the drive in the new gear, the pin 9 is moved to the right to allow the valve 18 to seat and cut off the vacuum from the conduit 26 to chamber 16, passage 89, chambers 87 and 83, and clutch conduit 102 and relieve them to atmosphere through a passage 12 and apertures 13, 14, a valve 22 sealing the end of the bore 12 first opening under the vacuum in the system to allow a certain amount of the vacuum to be relieved to provide an initial part engagement of the clutch, the full engagement then being provided by the leakage of air into the clutch cylinder 101 and/or through a small leakage aperture 129 in the valve 22. A smooth application of the clutch is thereby obtained which can be regulated by the operation of the accelerator pedal. The effect of the partial relief valve 93 may also be obtained by providing the chamber 91 of a relatively large capacity which would momentarily lower the vacuum in the clutch cylinder, the valve 93 being omitted. Alternatively, a simple throttling orifice could be provided for the chamber 91 instead of the valve. For gear changes in which it is necessary to retard a faster running clutch member, a brake device 130 for braking the more rapidly rotating gear clutch member, as described in British Specification 474,934, U.S.A. Specification 1,883,743, and German Specification 569,392, is provided.